I sat the LSAT a few years ago (got into my first choice, top tier school, then balked before hitting submit on my first year loan application and deferred for a year to work… I took an office manager job at a CPA firm because it paid well and had great benefits, and ended up sort of falling ass backwards into accounting). I'm sitting the CPA now.
IMO they're totally different beasts. The LSAT is not a knowledge based exam at all. I always referred to my prep as “practice” for the LSAT, and that's what it was. Learning strategies, practicing questions and organization methods, learning the language quirks, etc. It's about getting faster and more efficient for the most part – answering the questions quickly is what makes the difference for almost everyone. I did an in-person prep course for the LSAT which was a HUGE help. The practice felt more engaging and more rewarding, and there wasn't memorization required. I honestly enjoyed the LSAT prep to an extent (minus the worry about the test itself), while I'm despising CPA exam studying.
That said, the testing for the LSAT was waaaaaayyyy more stressful and anxiety provoking, because it's not pass-fail and you can't just keep taking it until you get a certain score. Someone puked in my exam room (well, they made it into the hallway at a run). One left in the middle. Multiple people were in tears at some point. The CPA exam felt chill and low-stakes in contrast. Of course then you get to take the Bar, which is like an awful combination of the two… knowledge based exam you have to study around the clock for for months and then extremely high stakes testing. A CPA will probably have a bit of a comparative advantage over other Bar candidates having had to do CPA exam prep.